The invention relates to a continuously operating, solid-jacket counterflow centrifugal extractor for the mixing together and separation of two liquids, having a centrifuge drum rotatable about a horizontal axis, provided with a mixing and contact zone between the two clarification zones, as well as separate inflows for carrying the liquids into the mixing and contact zone, and separate outflows leading away from the clarification zones.
A counterflow centrifugal extractor of this kind is known, for example, from German Auslegeschrift 10 37 417.
Counterflow centrifugal extractors are used for the purpose of transferring a dissolved extract contained in liquids from these liquids to liquid extractants in which the extract must be more soluble than it is in the liquid containing it. The transfer of the substance from the aqueous, extract-containing liquid to the extractant additionally presupposes a thorough mixing together or an intimate contact between the two liquids for the purpose of obtaining a high extraction yield. It is furthermore known that the number of extraction stages that can be achieved, and thus the extraction yield, is especially great, and the extraction can be performed with the least amount of extractant when the extraction process is performed countercurrently in the mixing and contact zone. Counterflow centrifugal extractors are preferred for liquid-to-liquid extraction, since the extraction of liquids containing solids leads to a rapid clogging of the extraction drums with sludge, so that they have to be shut down and cleaned, which requires a great deal of time and effort. To lengthen the running time of the extractors the solid-containing liquid, e.g., the culture broth used in the production of antibiotics, can be filtered to separate the solid components before the extraction.
The disadvantage of this method, in addition to the expense involved in the additional filtration, is that the solid components separated in the filtration are not subjected to the extraction and a great deal of extract is lost in the unextracted, moist solid matter.
German Auslegeschrift 10 37 417 shows a counterflow extractor in which the specifically lighter liquid is fed under higher pressure into the outer mixing and contact zone and the specifically heavier liquid is fed into the inner mixing and contact zone; the two liquids are carried countercurrently through a spirally disposed passage which is provided, for example, with holes to improve contact between the liquids.
While the specifically heavier liquid is being reclarified in a chamber in the outer area of the drum and being carried out of same, the specifically lighter liquid flows toward the axis of the extractor into an inner chamber for reclarification, and is again carried out of same.
The outer chamber additionally has a wall extending away from the axis at an angle, which reaches outwardly as far as the outlet for the heavier, solids-carrying liquid for the purpose of removing the centrifugally concentrated solids together with the specifically heavier liquid.
In this extractor, it is a disadvantage that only those solids can be carried out continuously with the specifically heavier liquid, which are either of lighter consistency or are able to be kept in suspension with the liquid and carried out in suspension form. This type of centrifugal extractor, however, is not suitable for discharging continuously solids which are of greater specific gravity than the specifically heavier liquid and which occur in relatively large quantities.
One-stage extractors are also known which are equipped, for example, with self-emptying centrifuge drums, the solids being carried out intermittently, but, for a great number of extraction processes, this one-stage extraction is not sufficient for achieving the desired extraction yield.
Therefore a plurality of one-stage extractors are connected in tandem and the liquid is conducted countercurrently in order to arrive at the desired number of stages and yield. Since in this method of operation, the solid matter which is centrifuged out and comminuted in this manner is fed to the next machine and has to be mixed with the rest of the liquid, emulsions are very frequently produced which can be separated but very poorly in the extractor, or only at additional expense, e.g., through the addition of wetting agents.